The present invention relates to an ink-jet printer head where conductive ink such as, for example, aqueous ink can be used and a method for manufacturing the same.
Conventionally, an ink-jet printer head which comprises a plurality of pressure chambers at least one portions of which are respectively formed of a piezoelectric material, a nozzle formed for each pressure chamber, and a voltage application means for the piezoelectric material, where an ink droplet is ejected from the nozzle by shear mode deformation of the piezoelectric material generated by applying a voltage to the piezoelectric material by the voltage application means has been known.
In Jpn. Pat. Appln. KOKAI Publication No. 8-52872, there has been disclosed an ink-jet printer head where an insulating film such as a parylene film is formed on an inner surface of an electrode inside a pressure chamber by CVD process or the like in order to prevent ink from deteriorating due to current flowing in the ink. According to the technology disclosed in the publication, driving voltage of the pressure chamber is electrically insulated from the ink by the insulating film so that, even when electrically-conductive ink is used, current can be prevented from flowing in the ink, thereby preventing the ink from deteriorating. According to the technology disclosed in the publication, it becomes possible to form an even film on a stacked piezoelectric member having a complex and fine shape such as an inner surface of the pressure chamber of the ink-jet printer head by forming an insulating film such as a parylene film by CVD process.
In Jpn. Pat. Appln. KOKAI Publication No. 8-290569, in order to improve stability and durability of a piezoelectric material, there has been disclosed an ink jet printer head where a voltage is applied to an electrode which is mounted on the piezoelectric material and whose portion to be inserted in the pressure chamber is over-coated with polyimide resin by spin coating process to display the piezoelectric material to a direction of a nozzle, so that ink is ejected from the nozzle. According to the technology disclosed in-the publication, ink is prevented from permeating the piezoelectric material by the polyimide resin so that the stability and durability of the piezoelectric material can be improved.
In Jpn. Pat. Appln. KOKAI Publication No. 10-291318, there has been disclosed such a technology that, in a nozzle formation, after a pressure chamber is attached with a plate, a nozzle is formed in the plate by irradiating the plate locally with an eximer laser or the like so that an ink jet printer head with excellent ink ejection performance can be provided. In this technology, when a nozzle is formed, such an organic film as a parylene film or a polyimide film is damaged by such laser light or beam as an eximer laser beam in the ultraviolet-range thereof, so that a portion of an electrode corresponding to the damaged portion of the film is directly exposed in the pressure chamber via the damaged portion. For this reason, since the insulation between the ink and the electrode is damaged, it becomes impossible to use electrically-conductive ink.
An object of the invention is to provide an ink-jet printer head where, when electrically-conductive ink such as aqueous ink is used, inconvenience such as degradation of the ink is not caused and an excellent ink ejection can be achieved, and a method for manufacturing the same.
An ink-jet printer head according to an aspect of the present invention comprises: a main body which has a plurality of pressure chambers to which ink is supplied, and a nozzle which is provided for each pressure chamber to cause the pressure chamber and the outside to communicate with each other, and whose portion is formed of a piezoelectric material;
an electrode which is provided in each pressure chamber and which applies a voltage to the piezoelectric material so as to change the volume of the pressure chamber to eject the ink via the nozzle;
an insulating film which covers a surface of the electrode in order to electrically insulate the electrode from the ink; and
a metal film which covers at least a portion of the insulating film which is in the pressure chamber and is near to the nozzle.
In such a head, the surface of the electrode exposed in the pressure chamber is covered with the insulating film to be electrically insulated from the ink. Therefore, even when electrically-conductive ink is used, the ink is prevented from degrading by current flowing in the ink. In this insulating film, a surface thereof which is near the nozzle and which may be irradiated by a laser beam for nozzle formation is protected by the metal film, not to, for example, be damaged by irradiation by the laser beam for forming the nozzle. This metal film does not cover the whole surface of the insulating film necessarily, but it may cover only a portion of the insulating film which is damaged easily, for example, a portion thereof which is in the vicinity of the nozzle. However, when the insulating film is formed of a material with poor chemical resistance, it is preferable that the entire surface of the insulating film be covered with the metal film. As a result, the insulating film can be prevented from being damaged by chemicals such as detergent in a cleaning material the insulating film has excellent chemical. When resistance, this metal film is not necessarily required to remain in a final product.
It is preferable that the insulating film be obtained by forming a film of an organic polymer material such as polyimide, polyurea, polyimide-amide, polyamide and/or polyazo-methylene by a deposition-polymerization process in view of adhesion with an electrode and resistance to ink and detergent. Particularly, when the insulating film is formed from polyurea, the temperature at which polymerization starts can be sufficiently reduced to the extent that polarization degradation of the piezoelectric material does not occur, so that it is made possible to cover the electrode with the film without degrading the performance of the piezoelectric material. Instead, when the insulating film is formed with polyimide, productivity can be improved because high-speed film formation can be achieved and polyimide is inexpensive. However, since polyimide has a high film formation temperature, it can be used effectively when heat-resistant PZT which is not degraded at a high temperature or the like is used as the piezoelectric material.
It is preferable that the metal film have a higher reflectivity because the insulating film can be protected from the laser beam. It is more preferable that the metal film have a reflectivity of 30% or more because a sufficient protective effect can be achieved even when the metal film is made thinner.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.